From: Barry Song <v-songbaohua@xxxxxxxx>
When an mTHP is added to the deferred_list due to partially mapped,
its partial pages are unused, leading to wasted memory and potentially
increasing memory reclamation pressure.
Detailing the specifics of how unmapping occurs is quite difficult
and not that useful, so we adopt a simple approach: each time an
mTHP enters the deferred_list, we increment the count by 1; whenever
it leaves for any reason, we decrement the count by 1.
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
---
Documentation/admin-guide/mm/transhuge.rst | 5 +++++
include/linux/huge_mm.h | 1 +
mm/huge_memory.c | 6 ++++++
3 files changed, 12 insertions(+)
diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index b78f2148b242..b1c948c7de9d 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -556,6 +556,11 @@ nr_anon
These huge pages could be entirely mapped or have partially
unmapped/unused subpages.
+nr_anon_partially_mapped
+ the number of transparent anon huge pages which have been partially
+ unmapped and put onto split queue. Those unmapped subpages are
+ also unused and temporarily wasting memory.